Process for controlling gear shifting in a cycle, and corresponding system and components

ABSTRACT

A system for controlling gear shifting in a transmission of a cycle, includes at least one gear wheel or sprocket on which a transmission element is engaged to perform transmission of motion as a result of movement in a predetermined direction. The gear shifting is carried out by changing the position of engagement of the transmission member with respect to the at least one gear wheel or sprocket. The system further includes at least one sensor for detecting the movement in corresponding direction of movement of the motion transmitting element for generating a signal and a control unit for controlling the change of the position of the element for transmitting motion with respect to the at least one gear wheel or sprocket when the signal indicates that the element for transmitting motion is moving in the given direction.

TEXT OF DESCRIPTION

[0001] The present invention tackles the problem of controlling gearshifting in cycles and has been developed with particular attention paidto the possible application to competition bicycles. In any case, thereference to this possible application, and in particular the referenceto the application to racing bicycles, must not be interpreted aslimiting the possible field of application of the invention.

[0002] Over the last few years there has developed, in the cycle sector,the tendency to associate to the cycle sensors of various nature so asto be able to acquire information of various kinds regarding theuse/behaviour of the means, the aim being to be able to intervenethrough actuators to modify—according to certain criteria, and actingboth in an automatic way and according to specific commands issued bythe user ? the conditions of use/behaviour of the means, in particularas regards its set.

[0003] In particular, the present invention has been developed withspecific reference to the servo systems which carry out positioning ofthe transmission chain of the cycle in a position corresponding to thefront derailleur and to the rear derailleur.

[0004] In drive trains mounted on cycles of a more sophisticated type itis envisaged that the toothing of the crankwheel and sprockets on whichthe derailleurs act are not all made up of teeth that are the same.Instead, the teeth are arranged in ordered sets and the teeth comprisedwithin each set have a sequence of differentiated geometries such as tofacilitate shifting of the chain, the foregoing in order to create,within the corresponding toothing, points or areas in which the movementof shifting of the chain is facilitated. Said points or areas arereferred to simply as “facilitating portions”.

[0005] If a command for shifting of the chain position is issued at aninopportune moment, the correct positioning of the chain may be at leastmomentarily hindered, and hence delayed.

[0006] This drawback, which is anyway noticeable in systems for controlof gear-shifting of a manual type, becomes particularly troublesome incycles in which the change of transmission ratio is controlled by anautomatically operated actuator, which is governed by an electroniccontrol system. Such a system is usually configured to co-ordinate thevarious interventions of modification of set of the cycle itself (bothaccording to the commands issued by the user and in an altogetherautomatic way), so as to optimize the performance of the cycle and, morein general, of the cycle-user system.

[0007] As is recognized, for example, in the European patent applicationEP-A-1 010 612 (on the other hand published after the date of priorityof the present application), in the framework of these systems, theattempt to control shifting of the chain at a wrong moment may give riseto various problems.

[0008] For example, in addition to an undesired retardation in actuationof the command, a problem may arise linked to the fact that the actuatorinvolved by the command ends up being activated (and hence absorbingenergy) for an interval of time in which the actuator itself is not ableto ensure that the action requested will be carried out. During thisinterval, the actuator absorbs power from supply sources (typicallybatteries) mounted on the cycle, this amounting to energy which, to alleffects, ends up being wasted without obtaining any useful result.

[0009] The aim of the present invention is to provide a solution that isable to overcome the drawbacks outlined above.

[0010] According to the present invention, this purpose is achievedthanks to a process having the characteristics specifically called forin the claims which follow.

[0011] The invention also relates to the corresponding system, as wellas to components usable in the context of the aforesaid system and/orfor implementation of the aforesaid process.

[0012] Basically, the solution according to the invention is along thelines of innovation that have led to an increasing sophistication in thecontrol systems usable on cycles, and in particular on competitionbicycles, with the aim of acquiring information that may be used foroptimizing the supply of energy, avoiding the waste that occurs insystems designed usually to be supplied via batteries, with the evidentneed to prevent the cycle from being rendered heavy by batteries thatare too cumbersome and/or weigh too much.

[0013] In a preferred embodiment, the solution according to theinvention involves using a transducer that may be positioned inalignment with the crank axle of the cycle. This is preferably atransducer of a potentiometric type, capable of detecting information,such as:

[0014] movement of the transmission element of the cycle (whether thisis a chain or a belt);

[0015] the corresponding direction of movement;

[0016] the angular position (or “phase”) of the corresponding toothingof the gear wheel driven by the crank axle of the cycle; and

[0017] the pedal cadence.

[0018] This information may be, at least in part, used to conditionactivation of members of the cycle moved by means of actuators whichdraw energy from power-supply sources, such as batteries mounted on thecycle itself.

[0019] This applies in particular as regards the operation of the frontand/or rear derailleur in order to obtain carrying-out of the shiftingoperation at the most favourable moment, i.e., when the chain is in aposition that exactly corresponds to one of the “facilitating portions”referred to in the introductory part of the present description.

[0020] In this connection, it should be noted that shifting of thechain, or more in general of the element for transmitting motion, maytake place properly only if the element itself is moving; otherwise,there is the risk of causing waste of energy and undesirable stresses onthe mechanical parts.

[0021] A pure and simple signal of movement is not, however, sufficient,given that, if the chain moves in a direction opposite to the desiredone (i.e., in the direction opposite to the direction of pedalling tomake the cycle advance), again an undesired result is obtained.

[0022] Consequently, the solution according to the invention in generalinvolves performance of the operation of gear shifting according towhether it is recognized that the chain itself is moving, and in thedesired direction (i.e., in the same direction as that of pedalling tomake the cycle advance), as well as to whether the gear wheel involvedin gear shifting is in a given angular position (in turn correspondingto the location of the chain in a position that corresponds to one ofthe aforesaid facilitating portions).

[0023] The invention will now be described, purely by way ofnon-limiting example, with reference to the attached drawings, in which:

[0024]FIG. 1 is a side elevation of a cycle, such as a competitionbicycle, equipped with a system according to the invention;

[0025]FIG. 2 is a top view of the cycle represented in FIG. 1;

[0026]FIG. 3 is a schematic view illustrating, as a whole, the structureof a sensor that may be mounted on the cycle represented in FIGS. 1 and2;

[0027]FIG. 4 illustrates the structure of another sensor that may bemounted on the aforesaid cycle;

[0028]FIGS. 5 and 6, each of which comprises two parts designated by a)and b), illustrate in greater detail the criteria of operation of thesensor of FIG. 4; and

[0029]FIG. 7 is a flowchart illustrating a possible example ofimplementation of the process according to the invention.

[0030] In the attached drawings, the reference number 1 designates, as awhole, a cycle, such as a competition bicycle, for example a racingbicycle.

[0031] The structural and constructional characteristics of such a cycleare to be deemed altogether known, and hence such as not to require adetailed description herein. In this connection, persons skilled in thesector will appreciate that the possibilities of use of the solutionaccording to the invention are certainly not limited to the type ofcycle illustrated.

[0032] In the currently preferred embodiment of the invention, the useis envisaged of a sensor 2 located in a position corresponding to thecrank axle C1. In embodiments of the invention considered lesspreferred, it is possible to envisage the use (either together with oras an alternative to the sensor 2) of a second sensor 3 located in aposition corresponding to the chain-tensioner.

[0033] The fact that in the drawings of FIGS. 1 and 2 the possibleco-presence of the sensors 2 and 3 is illustrated is therefore duesolely to the aim of not rendering the present description needlesslyburdensome.

[0034] The system further comprises two actuators, designated by 4 and5, designed to control, respectively, the front derailleur and the rearderailleur of the cycle.

[0035] Both the sensors 2 and/or 3 and the actuators 4, 5 are connected,for example by means of respective communication lines (not visible inthe drawings, but of a known type), to a processing unit 6 locatedpreferably, at least in part, in the vicinity of the handlebars of thecycle.

[0036] In its process and system aspects, the invention regards themodalities according to which the action of change of transmission ratioof the cycle is performed.

[0037] In a further aspect, the invention regards preferred solutionsfor obtaining the sensors 2 and 3.

[0038] In any case, at least in its process and system aspects, thesolution according to the invention is irrespective both of the specificcharacteristics of the sensors 2 and 3 and of the specificcharacteristics of the actuators 4 and 5.

[0039] Passing now to a detailed examination of the structure of thesensor 2 (FIG. 3), it may be noted that it basically comprises a statorelement 10, which includes for example a small disk made of electricallyinsulating material designed to be mounted in a fixed position withrespect to the frame of the cycle 1. In particular, the element 10 has acentral opening 12 through which it is possible to extend the crankpinH1 of the crank axle C1 of the cycle.

[0040] Provided on the element 10 are two concentric circular channelson strips 14 and 16, respectively outer and inner, both of which areelectrically conductive, and at least one of which (for example, thestrip 14, in the example illustrated) is made of electrically resistivematerial.

[0041] The two ends of the strip 14 terminate in two end pins,designated by 140 and 141, which may be connected respectively:

[0042] to a power-supply source V (it may, for instance, be one of thepower-supply batteries provided, in a known way, on the cycle), and

[0043] to a ground terminal G.

[0044] Connection of the pin 140 to the power source V is preferably bymeans of an electronic switch 150, the function of which will be betterexplained in what follows.

[0045] The inner strip 16, which is here supposed as being simply astrip, made of metal material, is connected to a further pin 142, whichmay in turn be connected to the processing unit 6.

[0046] Also connected to the same processing unit 6 is a further pin143, which is in turn connected to a pad 18 made of electricallyconductive material, the said pad being set between the strips 14 and 16at a point corresponding to one of the ends of the strip 14 itself.

[0047] Finally, the reference number 20 designates a rotating brush,made of electrically conductive material, mounted on a rotating member,which may be driven in rotation by the crankpin H1.

[0048] The set of parts described basically defines a voltage divider ofa resistive type, in which, once the value of the supply voltage Vapplied to the pin 140 has been set, the level of voltage detectable onthe pin 142 basically depends upon the angular position of the brush 20,and hence upon the angular position of the crankpin H1.

[0049] By sliding on both of the strips 14 and 16, the brush 20establishes an electrical connection between the strip 16 (which here isassumed as having a continuous circular development and being made ofelectrically conductive material) and the strip 14 (here configured asan open ring, with the two ends that are connected to the pins 140 and141 being adjacent but not connected to one another).

[0050] With every turn of the crankpin H1 of the bottom bracket, the pad18 and the pin 143 connected to it are short-circuited, for exampletowards the pin 141 and/or the end of the strip 14 connected thereto, soas to force the pin 143 to the ground voltage.

[0051] The output signal of the sensor 2 is basically a sawtooth signal,which assumes a maximum value when the crankpin H1 is in the angularposition corresponding to the location of the brush 20 at the end of thechannel 14 corresponding to the pin 140, and a minimum value (virtually,zero) when the crankpin H1 localizes the brush 20 at the opposite end ofthe channel 14, i.e., at a point corresponding to the pin 141.

[0052] The fact that the aforesaid sawtooth signal has an inclinedrising edge or an inclined falling edge evidently depends, given thesame position of installation of the sensor 2, upon the direction ofrotation imparted to the crank axle, and hence to the chain K.

[0053] In any case, with an appropriate operation of threshold-setting(carried out directly on the analog signal present on the pin 142, orelse on the numeric version obtained following upon an analog-to-digitalconversion in the transmission/acquisition phase by the unit 6), it ispossible to identify precisely whether the gear wheel to which thesensor is associated (in the example of embodiment here illustrated, thewheel moved by the crank axle) is in one of the angular positionscorresponding to the location of the chain K at one of the facilitatingportions, i.e., at the start of the sequence of teeth that facilitatethe shifting that it is intended to impart on the chain K.

[0054] In addition, again depending upon the aforesaid operation ofthreshold-setting, the unit 6 is able to verify that the output signalof the sensor 2 varies in time, an indication of the fact that thecorresponding gear wheel and the chain K drawn along by it are moving.Finally, detection of the slope (angular coefficient) of the leadingand/or trailing edges of the signal in question enables the unit 6 toidentify the direction of movement (forwards or backwards) of the chainK itself.

[0055] The set of parts described may be made in the form of anelectromechanical component basically resembling a normal rotatingpotentiometer, with the possibility of inserting the correspondingcomponent inside a shell or, in any case, in a protective structure (forexample, in a so-called “potting box”), so as to enable proper operationeven in a hostile environment, as is required by its envisagedinstallation in a position corresponding to the crank axle of a cycle.

[0056] Persons skilled in the sector will, on the other hand, appreciatethat the exemplary embodiment illustrated (which corresponds to anembodiment that is currently preferred) can undergo numerous variations,such as:

[0057] reversal of the role of the strips 14 and 16 (i.e., with thestrip 14 made altogether of a conductive material, and the strip 16 madeof a resistive material);

[0058] kinematic reversal of the roles of the brush 20 and of at leastone of the strips 14 and 16, namely, with the brush 20 mounted in astationary position and with one of the strips that rotates togetherwith the crankpin H1 of the crank axle; or

[0059] location of the pad 18 in a position corresponding to the end ofthe strip 14 connected to the pin 140; in this case, the passage of thebrush 20 in front of the pad 18 causes the pin 143 to be forced nolonger to the ground voltage but to the battery voltage V.

[0060] Yet further variant embodiments are evidently within the reach ofa person skilled in the sector, without prejudice to the possibility ofmaking a sensor of a potentiometric type that is able to supply atoutput (on the pin 142, in the exemplary embodiment illustrated) a firstsignal which uniquely identifies the angular position currently reachedby the crankpin H1 of the crank axle, with the further possibility ofgenerating a reference signal which indicates passage of the crankpin H1through a pre-determined angular position, as well as signalsidentifying movement and direction of movement of the chain K.

[0061] The sensor 3 is, instead, made in such a way as to be located ina position corresponding to the chain-tensioner normally provided in aposition corresponding to the rear end of the chain K of the cycle.

[0062] The chain-tensioner in question is usually made up of a pair ofoscillating arms or half-cages 22 provided with respective upper ends 24designed to be connected together at a point corresponding to a cagearticulation pin or pivot 26, which enables their installation on theframe of the cycle 1 with the possibility of oscillation about a pivotaxis X26 extending in the horizontal direction.

[0063] Mounted between the aforesaid upper ends, in such a way that itcan turn about its own axis X25, is a first top pulley or roller 25,usually having a lenticular profile.

[0064] The arms or half-cages 22 then have respective bottom ends 28designed to be connected together by means of a pivot 30, on which thereis mounted, in such a way that it can turn about its own axis X32, abottom pulley or roller 32 (usually having a lenticular profile).

[0065] The chain K of the cycle is mounted in such a way as to engage onthe top and bottom rollers 25 and 32 so that it describes a generalS-shaped path.

[0066] The possible movement of oscillation (in practice, of swinging)of the arms 22 about the axis X26 causes a corresponding movement of thebottom pulley or roller 32, with the result that the latter is able tokeep the chain K tensioned, absorbing and compensating the variations inthe path of movement of the chain K induced by the fact that the chainitself engages in different positions corresponding to the sprockets ofthe transmission of the cycle.

[0067] In any case, the set of parts that has just been described andthe corresponding criteria of operation correspond to solutions whichare of themselves amply known, and which consequently do not require anydetailed illustration herein, also because they are in themselvesirrelevant for the purposes of implementation and understanding of theinvention.

[0068] The invention envisages in fact configuring at least one of therollers 25, 32 (in the example of embodiment illustrated, the roller 32)as the rotor part of a sensor, the stator part of which, designated, asa whole by 34, is mounted on one of the arms or half-cages 22.

[0069] In the case in point, there is applied, on the roller 32(possibly by integration at the fabrication-process level, for exampleby means of co-moulding), an element 36 of magnetic material (such asplastoferrite) having, in the example here illustrated, a generalC-shaped conformation with a pre-determined angular extension, such asan angular extension of 180°.

[0070] The stator part 34 of the sensor preferably comprises two endinstruments or pickups 35, such as two Hall-effect sensors, or reedrelays, mounted on a corresponding arm or half-cage 22 in angularpositions staggered by 90° with respect to the axis of rotation X32 ofthe roller 32.

[0071]FIG. 5 illustrates, in its two parts set one above the other anddesignated by a) and b), a possible sequence of rotation of the element36 within a single turn of the roller 32, according to whether theroller 32 in question is moving (as viewed in FIG. 5) in a clockwisedirection (FIG. 5a) or in a counter-clockwise direction (FIG. 5b).

[0072] With reference to the direction of movement of the chain K, whichengages on the roller 32, the aforesaid two directions of rotation maybe considered as corresponding, respectively, to the forward movementand to the backward movement of the chain K itself.

[0073] It will be recalled that, as used within the present description,the term “forward” indicates the direction of movement of the chaincorresponding to the direction of movement imparted on the chain K whenthe crank axle of the cycle is driven in the direction that producesforward movement of the cycle itself.

[0074] Likewise, the two parts a) and b) of FIG. 6 represent two timingdiagrams corresponding to the behaviour of the output signals of the twoend instruments or pickups 35—the two signals being designated by 351and 352, which may be viewed collectively as a second signal—when thechain K moves, respectively, forwards (signals 351 and 352 of FIG. 6a)and backwards (signals 351 and 352 of FIG. 6b).

[0075] The aforesaid signals appear intrinsically as logic-type signals(i.e., as signals that present alternately a high logic level and a lowlogic level according to whether the respective end instrument or pickup35 is currently passing in front of the magnetic element 36 or is atsome distance from it).

[0076] Through a logic combination of the signals 351 and 352 generatedby the end instruments or pickups 35 it is possible to recognizeuniquely whether the movement of the roller 32 (and hence of the chainK) is taking place in one direction or the other. All this takes placeaccording to criteria that are in themselves amply known (for example,from the techniques of use of the so-called “optical encoders”), andconsequently does not require any specific illustration herein.

[0077] What has been previously said for the sensor 2 also applies tothe sensor 3. A person skilled in the sector is in fact able to define,on the basis of the indications provided previously, solutions that arefunctionally equivalent to the one just described.

[0078] In particular, the aforesaid sensing action may be carried out,for example, using the roller 25 instead of the roller 32, or else usingsensors or pickups 35 different from the ones described, or, yet again,using two sensors, one of which is associated to one roller and theother to the other roller.

[0079] It should, however, be said that, above all from thetechnological point of view (association to the roller 32 of an element36 of magnetic material), the solution just described provesparticularly advantageous in that it enables a simple, reliable sensorassembly to be obtained, which moreover affords low power consumptionand is able to operate properly even in a hostile environment, such asthat of the transmission of a cycle.

[0080] Again as regards power consumption, it has already been said thatthere may be associated to the sensor 2 (possibly, by directintegration) an element 150 which has the function of electrical switchable to interrupt connection of the sensor 2 to the voltage source Vwhen activation of the corresponding sensing function is not wanted.

[0081] In particular, when the switch 150 is in the open position, theresistive element represented by the strip 14 is not connected to thevoltage V, and hence there is no absorption of electrical energy.

[0082] The switch 150 is preferably connected to the unit 6 by means ofa respective line 151 in such a way as to cause the sensor 2 itself tobe in practice activated only when the unit 6 deems it necessary to haveavailable the corresponding signal.

[0083] This typically occurs when the unit 6 has available (eitherbecause it is received from outside as a result of a positive commandissued by the user of the cycle, or because it is processed by the unit6 itself according to the particular conditions of operation of thecycle) a command aimed at obtaining the change of transmission ratio ofthe cycle.

[0084] A similar arrangement may be provided, at the sensor 3, with aswitch 152 which activates the end instruments or pickups 35 onlyfollowing upon reception of a corresponding activation signal from theunit 6.

[0085] The modalities for carrying out the action of front-derailleurshifting will now be described with reference to the embodiment of theinvention currently preferred, i.e., assuming that only the sensor 2 ispresent, which is able to supply a signal that, processed by the unit 6,enables identification both of the angular position of the crank axle ofthe cycle, and hence of the gear wheel driven by the latter, andmovement and direction of movement of the chain K.

[0086] At the moment in which the need to carry out a change offront-derailleur gear ratio arises, the unit 6 activates the sensor 2(for example, by bringing the switch 150, typically represented by anelectronic switch, such as a transistor) into a closed position, so asto activate the sensor 2 itself. The corresponding output signal pickedup on the pin 142 enables the unit 6 to identify in a unique way theangular position reached by the crankpin H1 of the crank axle, as wellas the movement and the direction of movement of the corresponding gearwheel, and hence of the chain K.

[0087] The aim of what has been described above is to permit the unit 6to enable the corresponding actuator (in the example of embodimentillustrated, the actuator 4 associated to the front derailleur) withoptimal advance for obtaining the required shifting of the chainproperly; it having been detected simultaneously that the chain K ismoving forwards, thus preventing the start of any attempt atgear-shifting when the chain is stationary, or else when the chain ismoving backwards.

[0088] This operating mode is schematically illustrated in the flowchartof FIG. 7.

[0089] Here, starting from an initial step 100, the step 101 identifiesthe reception (or, in any case, processing) by the unit 6 of the requestfor a chain-positioning command, namely, for gear shifting.

[0090] The next step 102 is the one in which the unit 6 activates thesensor 2 so as to have available the corresponding signal.

[0091] After a selection step 103 (the function of which will beillustrated in what follows, and which is here assumed as having theoutput NO), the signal coming from the sensor 2 undergoes, in a step104, verification of whether the chain is actually moving.

[0092] The output NO from step 104 indicates that the chain K is notmoving.

[0093] In these conditions, the unit 6 goes back to step 103.

[0094] The output YES from step 104, instead, indicates that the chain Kis moving, and then, in a subsequent step 105, the unit 6 verifieswhether the signal coming from the sensor 2 indicates that the chain Kis moving forwards.

[0095] The output NO from step 105 causes return to step 103. In theevent of output YES from step 106, the unit 6 verifies, in a subsequentstep 106, whether the value of the signal of the sensor 2 is such as toindicate that the chain is in a position corresponding to one of shiftfacilitating portions.

[0096] Also in this case, in the event of an output NO, the unit 6returns to step 103. In the event of an output YES, instead, the unit 6sends, to the actuator 4, the command for gear shifting (step 107),whilst also deactivating the sensor. It then moves on to a an arreststep 108.

[0097] If, for the various reasons specified previously (chainstationary or else moving backwards, location in a position notcorresponding to a facilitating portion) there is a return to step 103,the unit 6 verifies whether the time elapsed from the moment in whichthe unit 6 itself received or processed the gear-shifting command signalis longer than a pre-determined threshold value equal to T.

[0098] If this interval is shorter than the threshold value (output NOfrom step 103), the unit 6 repeats the sequence of steps describedpreviously, in order to verify whether, in the meantime, the user hasstarted to pedal again and so to move the chain K forwards, inparticular bringing the chain into a position corresponding to one ofthe facilitating portions, so as to establish indications favourable forgear shifting.

[0099] If, instead, the conditions unfavourable for shifting of thechain persist for a certain time interval (output YES from step 103),the unit 6 moves onto a step 109, hence interpreting the gear-shiftingcommand received or processed as a non-executable command, possiblybecause it has been issued in an erroneous way, and so carries out areset to clear the gear-shifting command; then it moves on to an endstep 110.

[0100] In these conditions, for example, the unit 6 will be able tosend, to the user, a signal (for example an acoustic and/or lightsignal) aimed at pointing out the fact that, even though the user hasissued a command for gear shifting, he is behaving in a way which is notconsistent with the command given (for example, because he is notpedalling or he is pedalling backwards).

[0101] It will be appreciated that the criteria of operation describedabove are implementable, in a sub-optimal way, operating exclusivelyaccording to the signal of movement and direction of movement of thechain K, the foregoing being aimed at rendering the execution of thegear-shifting operation uniquely conditional on the fact that the chainK is moving forwards. In this case, evidently the information on theangular positioning of the gear wheel, and hence the information on thepositioning of the chain K with respect to the shift facilitatingportions, is not available.

[0102] Of course, without prejudice to the principle of the invention,the details of construction and the embodiments may vary widely withrespect to what is described and illustrated herein, without therebydeparting from the scope of the present invention. This applies inparticular to the possibility of applying the criteria of operationdescribed above with reference to the gear wheel associated to the crankaxle (and hence to the corresponding derailleur) also, or exclusively,to the rear derailleur.

[0103] At least in principle, it is also possible to envisage sensingthe position of the chain K, in particular the position with respect tothe toothing of the gear wheel moved by the crank axle, by exploitingthe signal generated by a sensor, such as the sensor 3, associated tothe chain-tensioner.

[0104] Yet a further possible variant embodiment may envisage use of thesensor 2 for generating the signal of angular position of the gearwheel, and use of the sensor 3 for generating the signal of movement anddirection of movement of the chain K. The solution based on the use ofthe sensor 2 alone proves, however, particularly advantageous in termsof precision and reliability of operation of the system.

1. A process for controlling gear shifting in the transmission of acycle comprising at least one gear wheel or sprocket on which atransmission member engages, which performs transmission of motion as aresult of its advance in a pre-determined direction; the gear shiftingbeing carried out by changing the position of engagement of saidtransmission member with respect to said at least one gear wheel orsprocket, the process comprising the operations of: detecting themovement and the corresponding direction of movement of said element fortransmitting motion; and controlling change of position of said elementfor transmitting motion with respect to said at least one gear wheel orsprocket when said element for transmitting motion is moving in saidgiven direction.
 2. The process according to claim 1 , for use in acycle in which said at least one gear wheel or sprocket has at least onegiven angular position in which shifting of said element fortransmitting motion is facilitated, the process comprising theoperations of: detecting the angular position of said at least one gearwheel or sprocket; and controlling change of position of said elementfor transmitting motion with respect to said at least one gear wheel orsprocket when the latter is in an angular position corresponding to saidat least one given angular position.
 3. The process according to claim 1, comprising the operations of providing sensor means for detecting atleast one quantity comprised in the group consisting of: the angularposition of said at least one gear wheel or sprocket; and the movementof said element for transmitting motion and the corresponding directionof movement; and further comprising the operation of selectivelyactivating said sensor means according to a command request for changingthe position of said element for transmitting motion with respect tosaid at least one gear wheel or sprocket.
 4. The process according toclaim 2 , wherein said at least one gear wheel or sprocket is associatedto the crank axle of said cycle, and in that said at least one pre-setshift position corresponds to at least one set of teeth of said gearwheel or sprocket.
 5. The process according to claim 1 , comprising theoperations of detecting the movement and corresponding direction ofmovement of said element for transmitting motion in at least oneposition chosen between the crank axle of the cycle and a tensioningelement associated to said element for transmitting motion.
 6. A systemfor controlling gear shifting in a transmission of a cycle, comprisingat least one gear wheel or sprocket on which is engaged a transmissionelement that performs transmission of motion as a result of its advancein a pre-determined direction; the gear shifting being carried out bychanging the position of engagement of said transmission member withrespect to said at least one gear wheel or sprocket, the said systemcomprising: at least one sensor for detecting the movement andcorresponding direction of movement of said motion-transmitting elementand for generating a respective signal; a control unit for controlling,starting from said respective signal, the change of the position of saidelement for transmitting motion with respect to said at least one gearwheel or sprocket when said signal indicates that said element fortransmitting motion is moving in said given direction.
 7. The systemaccording to claim 6 , for use in cycle in which said at least one gearwheel or sprocket has at least one given angular position in which theshifting of said element for transmitting motion is facilitated, whereinsaid at least one sensor generates a corresponding signal indicating theposition of said at least one gear wheel or sprocket; and said controlunit is configured for controlling, starting from said respectivesignal, the change of the position of said element for transmittingmotion with respect to said at least one gear wheel or sprocket whensaid at least one gear wheel or sprocket is in an angular positioncorresponding to said at least one given angular position.
 8. The systemaccording to claim 6 , further comprising at least one switch forselective activation of said at least one sensor according to a commandfor changing the position of said element for transmitting motion withrespect to said at least one gear wheel or sprocket.
 9. The systemaccording to claim 7 , wherein said at least one gear wheel or sprocketis associated to the crank axle of said cycle and in that said at leastone facilitating angular position corresponds to at least one set ofteeth of said gear wheel or sprocket.
 10. The system according to claim6 , wherein said at least one sensor is configured for being associatedto the crank axle of said cycle and/or to a tensioning element fortensioning said element for transmitting motion.
 11. A sensor forimplementation of a process for controlling gear shifting in thetransmission of a cycle comprising at least one gear wheel or sprocketon which a transmission member engages, which performs transmission ofmotion as a result of its advance in a pre-determined direction; thegear shifting being carried out by changing the position of engagementof said transmission member with respect to said at least one gear wheelor sprocket, the process comprising the operations of: detecting themovement and the corresponding direction of movement of said element fortransmitting motion; and controlling change of position of said elementfor transmitting motion with respect to said at least one gear wheel orsprocket when said element for transmitting motion is moving in saidgiven direction, the sensor comprising: a stator element which can beassociated to the crank axle of said cycle in a fixed position withrespect to the frame of the cycle itself; and a rotor element which canbe associated, in a relationship of being drawn along in rotation, tosaid crank axle; said stator element and said rotor element definingtogether a potentiometric voltage divider adapted to be supplied with asupply voltage and is able to supply at output a signal indicating theangular position of said rotor element with respect to said statorelement.
 12. The sensor according to claim 11 , wherein associated toone of said stator element and said rotor element is at least oneelement of an electrically resistive material, and in that associated tothe other of said stator element and said rotor element is a contactelement which is able to co-operate with said resistive element in sucha way as to create a voltage divider in which the value of the outputsignal of the voltage divider depends upon the position of said contactelement with respect to said resistive element.
 13. The sensor accordingto claim 12 , wherein in that associated to one of said stator elementand said rotor element is a further contact element defining the outputpoint of said voltage divider, and wherein said contact element acts ina sliding relationship with said resistive element and with said furthercontact element.
 14. The sensor according to claim 12 , wherein saidresistive element is in the form of an open ring with the correspondingends to which a biasing signal of said resistive element may be applied.15. The sensor according to claim 13 , wherein said further contactelement has an annular and closed shape.
 16. The sensor according toclaim 14 , wherein said further contact element has an annular andclosed shape and wherein said resistive element and said further contactelement are concentric.
 17. The sensor according to claim 11 , furthercomprising a reference contact element which is able to generate a levelof a given signal when said rotor element is positioned at a given anglewith respect to said stator element.
 18. The sensor according to claim14 , further comprising a reference contact element which is able togenerate a level of a given signal when said rotor element is positionedat a given angle with respect to said stator element and wherein saidreference contact element is located in a position corresponding to oneof the respective ends of said resistive element.
 19. The sensoraccording to claim 11 , comprising a switch element selectivelyswitchable between: a first operating position, in which said voltagedivider is connected to a supply source; and a second position, in whichsaid voltage divider is disconnected from said supply source inconditions such that energy absorption by the sensor (2) issubstantially zero.
 20. A movement sensor for detecting the movement andthe corresponding direction of movement of an element for transmittingmotion in a transmission of a cycle, the sensor comprising: at least onerotary body which can be driven in rotation about a respective axis bysaid element for transmitting motion; a marker element mounted on saidat least one rotary body (32); and at least one pickup mounted in aposition facing said rotary body and capable of generating at least onerespective signal indicating the fact that, as a result of the rotationabout said respective axis of said rotary body, said marker element isin a position facing the detected element itself.
 21. The sensoraccording to claim 20 , wherein said marker element has, when it ismounted on said rotary body, an angular extension of 180° with respectto said respective axis of rotation.
 22. The sensor according to claim21 , comprising two pickups set at a given angle apart from one anotherwhere the vertex of the said angle lies on said axis of rotation. 23.The sensor according to claim 22 , wherein said two pickups are set atan angle of 90° apart from one another where the vertex of the saidangle lies on said axis of rotation.
 24. The sensor according to claim20 , wherein said marker element is made of magnetic material, such asplastoferrite.
 25. The sensor according to claim 20 , wherein saidrotary body is a pulley associated to the chain-tensioner of a cycle,and in that said marker element is incorporated in said pulley.
 26. Thesensor according to claim 20 , wherein said pickup is mounted on thesupporting element that supports said rotary body.
 27. The sensoraccording to claim 25 , wherein said pickup is mounted on the supportingelement that supports said rotary body and wherein said supportingelement is one of the half-cages or arms of the chain-tensioner of thecycle.
 28. The sensor according to claim 20 , wherein said pickup is aHall-effect sensor or a reed relay.